As higher efficiency for low power applications is sought, more and more linear regulator solutions are being replaced by switching regulator solutions. However, limitations of present technology switching regulators generally are limited to monitoring the VIN/VOUT ratio. When using current sensing to control the switching regulator power supply, significant delays may exist when measuring input current for generating values for sensed current especially when a high voltage regulator of the switched power supply is operating at very low duty cycles. Current sensing precision is critical in high performance, high voltage switching regulators.
Referring to FIG. 2, depicted is a simplified schematic diagram of a prior technology switching power transistor and current sensing circuit. This circuit has been used in high voltage, non-synchronous, high-side drive switching regulator circuits like the one shown in FIG. 1. The basic principle of current sensing is to measure the current flowing in a sensing transistor 548 that is biased under the same conditions as the power switching transistor 200. The measured current is weighted by an aspect ratio between the power switching transistor 200 and sensing transistor 548, usually in the range of from about 1/1000 to about 1/10,000 . A current conveyor (540, 546) is used for forcing the voltage across the sensing transistor 548 to be equal to the voltage of the power switching transistor 200. During operation the voltage across the power switching transistor 200 varies a lot depending whether the power switching transistor 200 is “on” or “off,” and the switching slopes are very fast (very high dv/dt). The current conveyor must follow the voltage on power switching transistor 200, that a significant loss of accuracy is induced as well as measured noise. Switching noise increases and accuracy decreases with the transfer ratio of the DC/DC converter.